Method of forming tapered contact openings

Abstract

Tapered openings are formed in silicon oxide layers on a substrate by first saturating the silicon oxide layers with water, such as by immersing the substrates and the silicon oxide layers in water. The silicon oxide layers are then heated to dehydrate them to a desired water content at which a desired adhesion of a resist layer to the silicon oxide layer is achieved. A photoresist layer is then coated on the silicon oxide layers and photolithographically defined to provide them with openings therethrough over the area of the silicon oxide layers where the tapered openings are to be provided. The exposed area of the silicon oxide layers are then etched with an etchant for silicon oxide, such as buffered hydrofluoric acid, containing a component for lifting the edge of the resist from the silicon oxide, such as an acid, to etch tapered openings through the silicon oxide layers. Saturating the silicon oxide layers with water and then dehydrating them ensures that the openings have walls of uniform taper etched therethrough.

I claim: 
     
       1. In a method of etching tapered openings in a layer of silicon oxide or a substrate wherein a layer of a resist is coated on the silicon oxide layer, the resist layer is provided with an opening therethrough to expose a portion of the silicon oxide layer and the silicon oxide layer is etched such that the edge of the resist layer is lifted from the silicon oxide layer to cause a tapered opening to be etched through the silicon oxide layer, the improvement comprising the step of prior to coating the silicon oxide layer with the resist, substantially saturating the silicon oxide layer with water, and then heating the silicon oxide layer to dehydrate the silicon oxide layer a desired amount such that all of the silicon oxide layer is dehydrated to substantially the same moisture level.   
     
     
       2. A method in accordance with claim 1 in which the silicon oxide layer is saturated with water by immersing the silicon oxide in water for a period long enough to ensure saturation. 
     
     
       3. A method in accordance with claim 2 in which the silicon oxide layer saturated with water is heated to dehydrate the 1ayer to an amount which provides a desired adhesion of the resist layer on the silicon oxide layer. 
     
     
       4. A method in accordance with claim 3 in which the silicon oxide layer is dehydrated by heating at about 200° C. for about 30 minutes. 
     
     
       5. A method in accordance with claim 4 in which the resist is a negative photoresist. 
     
     
       6. A method in accordance with claim 2 in which the silicon oxide layer is etched with an etchant containing a component for etching the silicon oxide and a component for lifting the resist. 
     
     
       7. A method in accordance with claim 6 in which the component of the etchant for etching the silicon oxide is a mixture of hydrofluoric acid and ammonium fluoride and the component for lifting the resist is an acid. 
     
     
       8. A method in accordance with claim 7 in which the component of the etchant for lifting the resist is an acid selected from the group consisting of nitric acid, phosphoric acid and acetic acid. 
     
     
       9. A method in accordance with claim 6 in which the etchant is a mixture of by volume 4 parts concentrated hydrofluoric acid, 25 parts ammonium fluoride (48% concentration) and 11 parts acetic acid. 
     
     
       10. A method in accordance with claim 9 in which the resist is a negative photoresist.